1. Field of the Invention
This invention relates to a heat radiation shielding component dispersion used in producing heat radiation shielding forms (extruded or molded forms) containing a heat radiation shielding component, or producing heat radiation shielding products such as heat radiation shielding films formed by coating on transparent substrates of various types such as glass and resin a heat radiation shielding film forming coating liquid, and also relates to a process for preparing such a dispersion. More particularly, this invention relates to a heat radiation shielding component dispersion that can be free of any various restrictions as a dangerous object during transportation and also can not easily cause formation of a sediment caused by agglomeration of the heat radiation shielding component during storage, and relates to a process for preparing such a dispersion, and a heat radiation shielding film forming coating liquid, a heat radiation shielding film and a heat radiation shielding resin form which are obtained using such a dispersion.
2. Description of the Related Art
Solar radiations which enter various buildings and vehicles through their “openings” such as windows and doors include visible-light rays and besides ultraviolet radiations and infrared radiations. Among the infrared radiations included in such solar radiations, near-infrared radiations of 800 to 2,500 nm in wavelength are called heat radiations, and enter through the opening to cause a temperature rise in the room. In order to avoid such a temperature rise, in recent years, in the field of window materials for various buildings and vehicles, there is a rapid increase in demand for heat radiation shielding products which can shield heat radiations while taking in visible-light rays sufficiently and can prevent the temperature rise in the room while keeping brightness. Patents concerning such heat radiation shielding products are proposed in a large number.
For example, a heat radiation shielding sheet is proposed in which a heat radiation reflecting film comprising a transparent resin film on which a metal or a metal oxide has been vacuum-deposited is bonded to a transparent substrate such as a glass sheet, an acrylic sheet or a polycarbonate sheet (see Japanese Patent Applications Laid-open No. 61-277437, No. 10-146919, No. 2001-179887, etc.). However, this heat radiation reflecting film has a disadvantage that the film itself is very expensive and also requires a complicate process having a bonding step and so forth, resulting in a high cost. In addition, the heat radiation shielding sheet has a disadvantage that the adherence between the transparent substrate and the heat radiation reflecting film is not so good as to cause peeling of the film as a result of changes with time.
Heat radiation shielding sheets in which metals or metal oxides are directly vacuum-deposited on the surfaces of transparent substrates are also proposed in a large number. These, however, have a problem that, in producing such heat radiation shielding sheets, an apparatus is necessary which requires environment control in a high vacuum and in a high precision, resulting in a bad mass productivity and poor general-purpose properties.
Besides, also proposed are, e.g., a heat radiation shielding sheet, and a film used therefor, in which an organic infrared absorber typified by a phthalocyanine compound or an anthraquinone compound is kneaded into a thermoplastic transparent resin such as polyethylene terephthalate resin, polycarbonate resin, acrylic resin, polyethylene resin or polystyrene resin (see Japanese Patent Applications Laid-open No. 6-256541, No. 6-264050, etc.). However, in order to shield the heat radiations sufficiently, the infrared absorber must be mixed in a large quantity. Its mixing in a large quantity leaves a problem that the ability to transmit visible light rays may lower. Also, since an organic compound is used, their use in window materials or the like for buildings and vehicles which are always directly exposed to sunlight involves a difficulty in weatherability, and can not necessarily said to be appropriate.
Further proposed is, e.g., a heat radiation shielding sheet in which inorganic particles of titanium oxide having heat radiation reflectivity or mica or the like coated with titanium oxide are kneaded into a transparent resin such as acrylic resin or polycarbonate resin (see Japanese Patent Applications Laid-open No. 5-78544, No. 2-173060, etc). Such a sheet, however, requires addition of heat radiation reflecting particles in a large quantity in order to improve heat radiation shielding power, so that the visible-light transmission properties may lower with an increase in the quantity of the heat radiation reflecting particles mixed. On the other hand, the addition of heat radiation reflecting particles in a small quantity may bring an improvement in the visible-light transmission power but may result in a low heat radiation shielding power. Thus, there has been a problem that it is difficult to satisfy the heat radiation shielding power and the visible-light transmission power simultaneously. In addition, the mixing of heat radiation reflecting particles in a large quantity involves a problem in view of strength that substrates transparent resins may have low physical properties, in particular, a low impact resistance and a low toughness.
Under such technical backgrounds, the present applicants have taken note of hexaborides, which have free electrons in a large quantity, and have already proposed i) a heat radiation shielding film forming coating liquid having been so made up that fine particles of this hexaboride are dispersed as a heat radiation shielding component in an organic solvent and a binder of various types is added thereto, and ii) a heat radiation shielding film obtained by coating a transparent substrate of various types with this coating liquid, followed by curing (see Japanese Patent Applications Laid-open No. 11-181336, No. 2000-96034 and No. 2000-169765).
However, in such a technique, the coating liquid is made up presuposing a form in which the fine hexaboride particles are dispersed in an organic solvent. In this relation, there has been a problem that heat radiation shielding film forming coating liquids are handled as dangerous objects according to the Fire Services Act and are restricted in variety when the heat radiation shielding film forming coating liquids are transported, resulting in relatively high transportation cost.
As another problem, when dispersions in which the fine hexaboride particles stand dispersed as a heat radiation shielding component in an organic solvent are stored for a long term, the fine particles tend to agglomerate one another because of the Brown movement of fine particles (colloid particles) to cause a sediment in some cases.
As still another problem, when the fine hexaboride particles are kneaded into a transparent resin material to make an extruded or molded form, the fine hexaboride particles must uniformly be kneaded into the transparent resin material, removing the organic solvent in the state the fine hexaboride particles are dispersed in the solvent, and hence this can not necessarily be said to be the best method because the equipment and process used must be complicate.